Fluid testing covers a large variety of tests aimed at detecting the presence of specific fluids or identifying certain fluids. Fluid testing may include, for example, water purity tests, industrial quality tests, and aviation fuel purity tests.
Checking the quality of aviation fuel is a routine practice. Poor fuel quality may lead to loss of engine power, possibly resulting in an aviation accident. Aviation regulations stipulate that fuel should be checked daily by ground personnel, and as part of the preflight checks performed by a pilot. With some aircraft (such as, for example small airplanes), these checks are performed by taking samples directly from the fuel system. For example, a fuel sample is typically collected from the bottom of the fuel tank into an ampoule. The sample in the ampoule is then checked visually. A typical procedure for checking for water in the fuel is based on a visual detection of the difference in color between water and fuel. Such a visual determination may be dependent on a subjective interpretation of the visual results. Interpretation of the results may be affected by such factors as, for example, illumination of the sample, the experience of the pilot or other person performing the check, and the condition of the ampoule.
Fuel may also be visually checked for other properties. For example, since aviation fuel is typically dyed to indicate the type and grade of the fuel, the color of the fuel may be compared against known fuel colors.
Checking the quality of the fuel may be assisted by an appropriate optical device. For example, the index of refraction of fuel may be different than the index of refraction of water. In addition, the indices of refraction of various types or grades of fuel may differ from one another. Thus, an appropriate device that is sensitive to index of refraction may be used to assist in checking fuel quality. In order to reduce subjectivity in interpreting the results, it may be advantageous if the device were automated. An automated device may give an automatically generated indication as to whether or not the fuel quality is acceptable.
Gan, in WO 2005/050179 and in US 2009/0128803, has described optical devices that may be used to check for deviation of the index of refraction of a fluid from an expected value. In the described optical devices, the fluid to be checked is introduced into the optical path of a device in which two or more gratings or similar patterns are observed. Light passing through the gratings and the fluid form a moiré pattern. The details of the moiré pattern formed by the device are sensitive to the index of refraction of the fluid. Therefore, visual or automated comparison of the observed moiré pattern with a reference moiré pattern may indicate whether the index of refraction has an expected value. However, automated comparison of moiré patterns may require a complex comparison device and algorithm. In addition, an automated moiré pattern comparison may be sensitive to variable factors other than index of refraction.
Gan et al. in US 2009/0153846 describe an optical dipstick device that may be lowered into a fluid. In the optical dipstick device, the end of the dipstick is inserted into a container for containing a fluid. The optical path from a light source to a detector or to a detector array in the dipstick depends on the optical properties of the contents of the container. Thus, a detector signal may be interpreted to indicate the quantity of fluid present in the container, and whether the index of refraction of a fluid in the container matches an expected value. However, such a dipstick device may be inconvenient for use with a typical fuel ampoule.
It is an object of the present invention to provide a device for automatic optical checking of fuel quality.
Other aims and advantages of the present invention will become apparent after reading the present invention and reviewing the accompanying drawings.